CA1206688A

CA1206688A - Succinic anhydride derivatives as a scorch inhibitor for carboxylated rubbers

Info

Publication number: CA1206688A
Application number: CA000427250A
Authority: CA
Inventors: Donald C. Grimm
Original assignee: Goodyear Tire and Rubber Co
Current assignee: Goodyear Tire and Rubber Co
Priority date: 1982-05-17
Filing date: 1983-05-03
Publication date: 1986-06-24
Also published as: JPS58210942A; DE3365100D1; EP0094900B1; EP0094900A1; US4415690A; JPH0320420B2; BR8302320A

Abstract

ABSTRACT OF THE DISCLOSURE
SUCCINIC ANHYDRIDE DERIVATIVES AS A
SCORCH INHIBITOR FOR CARBOXYLATED RUBBERS

Scorch (the premature cross-linking of an elastomer) is a problem that is often encountered in carboxylated rubbers. Succinic anhydride derivatives (alkenyl succinic anhydrides, alkyl succinic anhydrides, and their corresponding dicarboxylic acids) can be used to greatly improve the scorch resistance of carboxylated rubbers. These succinic anhydride derivatives can be distributed throughout a carboxylated rubber before or after coagulation using any procedure that will result in a thorough mixing to form a rubber composition with improved scorch resistance.

Description

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SUCCINIC ANHYDRIDE DERI~ATIVES AS A
SCORC~I INHIBITOR FOR CARB XYLATED RUBBERS

Background of the Invention ~ arboxylated rubbers (rubbers containing carboxyl groups in their polymer chain) are useful for many purposes. Carboxylic nitrile rubber (XNBR) is a terpolymer of butadiene, acrylonitrile, and methacrylic acid. This carboxyl modification of nitrile rubber (NBR) produces a material that has outstanding abrasion resistance. Metal oxide vulcanizates of carboxylic elastomers also have unusually high tensile strengths, superior ozone resistance, and elevated modulus values. Such carboxyl modification of a rubber typically involves the addition of about ,75 percent to 15 percent by weight of an unsaturated carboxylic acid of the acrylic acid type to the monomer charge compos-ition of the carboxylic rubber being synthesized.
These carboxylated elastomers can be vulcanized in a manner analogous to their uncarboxylated counterpart utilizing a sulfur curing agent. In addition to this, if a polyvalent radical and particularly divalent metals are available in the vulcanization recipe, the carboxyl groups in the polymer chain can take part in this cross-linking reaction. This cross-linking reaction is fast in the presence of divalent metals and scorch problems are often encountered. Even at room temperature, carboxylated rubbers will often cure in 48 hours or less in the presence of zinc oxide when uninhibited. Since scorch (the p:re-mature cross-linking of an elastomer) can render a rubber completely unworkable, it is necessary to control this cross-linking reaction between carboxyl groups on the polymer chain. This invention discloses the use of alkenyl succinic anhydride and alkyl succinic anhydride as agents to greatly improve the scorch resistance of carboxylated rubbers.

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The_Invention Alkenyl succinic anhydrides, alkyl succinic anhy-drides and their corresponding dicarboxylic acids can be used as scorch inhibitors in a~y carboxylated rubber. This invention discloses an improved scorch resistant carboxylated rubber composition comprising:
a carboxylated rubber and at least one succinic anhy-dride derivative selected from the group consisting o~
succinic anhydrides having the O
stru~tural formula: R - CH - C~
O

a wherein R is an alkenyl moiety containing from 8 to 25 carbon atoms, inclusive; dicarboxylic acids having the structural formula:

R - CH- C - OH
CH2~C - OH

wherein R is an alkenyl moiety containing from 8 to 25 carbon atoms, inclusive; alkyl succinic anhydrides having the structural formula.
O
Z - CH- C o o wherein Z is an alkyl moiety containing from 8 to 25 carbon atoms, inclusive; and dicarboxylic acids having the structural ~ormula: O
Z - CH - C - OH

a wh~rein Z is an alkyl moie-ty containing from 8 to 25 carbon a-toms, inclusive, which is distributed -throughout said carboxylated rubber composition as a scorch inhibitor.

These carboxylated rubbers (elastomers) contain chain linkages derived ~rom unsaturated carboxylic acids o~ the acrylic acid type. Some representative examples of unsaturated carboxylic acids o~ the acrylic acid type include acrylic acid, methacrylic acid, sorbic acid, ~-acryloxypropanoic acid, ethacrylic acid, 2-ethyl-3-propyl acrylic acid, vinyl acryllc acid, cinnamic acid, maleic acid3 fumaric acid, and the like. The rubbers ~or which these agents are useful as a scorch inhibitor generally contained from about.75 percent to 15 percent by weight chain linkages which are derived from unsaturated carboxylic acids.
These carboxylic rubbers can be synthesized using any conventional polymerization technique. Emulsion polymerization of carboxylated elas-tomers is generally preferred and is used almost exclusively in industrial production. This type of a synthesis generally utilizes a charge composition comprising water, monomers, an initiator, and an emulsifier (soap). Such polymerizations can be run over a very wide temperature range from about 0C. to as high as 100C. Very good results have been obtained when polymerizations are run at a temperature from about 5C. to 60C.
The amount o~ carboxylic monomer (unsaturated carbox-ylic acid of the acrylic acid type) incorporated in acarboxylated rubber may be varied over a wide range. The monomer charge ra-tio between the carboxylic monomer and the comonomers employed in a polymerization may also be varied over a very wide range. A typical monomer charge compositlon for a carboxylated nitrile rubber is 67 percent butadiene, 26 percent acrylonitrile, and 7 percent meth-aorylic acid (percentages are by weight). Some other mo~omers that may be copolymerized with a carboxylic monomer to ~orm elastomers for which succinic anhydride der-ivatives are use~ul a9 a scorch inhibitor include styrene;isoprene; vinylidene monomers having one or more terminal CH2 = C' groups; vinyl aromatics such as ~-me-thylstyrene, bromostyrene, chlorostyrene, fluorostyrene, vinylphenol, ~ ~o~

3-hydroxy-4-methoxystyrene, vinylanisole, ~-nitrostyrene, and the like; a-olefins such as ethylene; vinyl halides, such as vinylbromide, chloroethene (vinylchloride), vi~yl-fluoride, vinyliodide, 1,2-dibromoethene, l,l-dichloro-ethylene (vinylidene chloride), 1,2-dichloroethylene, and the like; vinyl esters such as vinyl acetate; aS~-olefinically unsaturated nitriles, such as methacrylo-nitrile; a,~-olefinically unsaturated amides such as acrylamide, N-methyl acrylamide, N-t-butyl acrylamide, N-cyclohexyl acrylamide, diacetone acrylamide, methacryl-amide, N-ethyl methacrylamide, and the like; ~ ole~in-ically unsaturated N-alkylol amides having the general structural formula: 0 CH2=C-C-N-(CH2)X-OH
R H
wherein R is a hydrogen atom or an alkyl grou-p containing from l to 4 carbon atoms and x is an integer from 1 to 4 inclusive such as N-methylol acrylamide, N-ethylol acryl-amide, N-propylol acrylamide, N-methylol methacrylamide, N-ethylol methacrylamide, and the like; vinyl pyridine;
n-octyl methacrylate, dodecyl methacrylate, ~methyl ethacrylate, and ethyl-ethacrylate; haloalkyl acrylates such as chloropropyl acrylate; methacrylates; hydroxyethylacrylate; and poly-functional compounds such as ethylene glycol dimethacryl-ate, diethylene glycol diacrylate, divinylbenzene, alkenyl pen-taerythri-tol, methylene-bis-acrylamide, and the like.
In the polymerization of unsaturated carboxylic acids, of the acrylic acid type with one or more of the above-mentioned monomers, there can be competing or side reactionswhich take place. Therefore, the choice of reactants, process conditions, order of addi-tion of reactants and the -li.ke, ~hould be selected in order to produce a useful rubber containing carbo~Jl groups. The monomers employed and monomer ratios used in the charge composition for -the polymerization should be selected in a manner that will produce a carboxylated elastomer. It should be noted ~2~

that many combinations of the above-mentioned monomers ~,rill result in the polymerization of a nonelastomeric polymer.
The carboxyl modified polymers which are generally preferred include carbox~lated nitrile rubber, which is a copolymer 5 of butadiene, acrylonitrile, methacrylic acid; terpolymers of methacrylic acid, styrene, and butadiene; copolymers of methacrylic acid and butadiene; copolymers o~ methacrylic acid and isoprene; terpolymers of acrylic acid, acrylo-nitrile 9 and butadiene; and terpolymers of methacrylic 10 acid, vinylidene chloride, and butadiene.
The emulsifiers used in the polymerization of such polymers may be charged at the outset of the polymerization or may be added incrementally or by proportioning as the reaction proceeds. Generally, anionic emulsifier systems provide good results, however, any of the general types of anionic, cationic or nonionic emulsifiers may be ernployed in the polymerization.
Among the anionic emulsifiers that can be employed in e~ulsion polymerizations are fatty acids and their alkali metal soaps such as capr~lic acid, capric acid, pelargonic acid, lauric acid, undecylic acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, and the like; amine soaps of fatty acids such as those formed from ammonia, mono-and di-alkyl amines, substituted hydra-zines, guanidine, and various low molecular weight diamines;chain-substituted derivatives of fatty acids such as those having alkyl suhstituents; napthenic acids and their soaps and the like; sulfuric esters and their salts, such as the tallo~ alcohol sulfates, coconut alcohol sul~ates, fatty alcohol sulfates, such as oleyl sulfate, sodium lauryl sulfate and the like; sterol sulfates; sulfates of alkylcyclohexanols,sulfation products of lower polymers of ethylene a.s C10 to C20 straight chain olefins, and o-kher hydrocarbon mixtures, sulfuric esters of aliphatic and aromatic alcohols hav.ing in-termediate linkages, such as ether, ester, or amide groups such as alkylbenzyl (polyethyleneoxy) alcohols, the sodium salt of tridecyl ether sulfate; alkane sulfonates, esters and salts, such as alkylchlorosulfonates with the general formula RS02Cl, ~06~

wherein R is an alkyl group having from 1 to 20 carbon atoms, and alkylsulfonates with the general fo-rmula RS02-OH, wherein R is an alkyl group having from 1 to 20 carbon atoms; sulfonates with intermediate linkages such as ester and ester-linked sulfonates such as those having the formula RCOOC2~4S03H and ROOC-CH2-S03H, wherein R is an alkyl group ha~ing from l to 20 carbon atoms such as dialkyl sulfo-succinates; ester salts with the general formula:
O O
t~\ ,. ., ~C-CH-CH2-C-O-R
SO~Na wheréin R is an alkyl group having from 1 to 20 carbon atoms; alkarylsulfonates in which the alkyl groups contain preferably from 10 to 20 carbon atoms, e.g. dodecylbenzene-sulfonates, such as sodium dodecyl~enzenesulfonate; alkyl phenol sulfonates; sulfonic acids and their salts such as acids with the formula RS03Na, wherein R is an alkyl and the like; sulfonamides; sulfamido methylenesulfonic acids; rosin acids and their soaps; sulfonated derivatives of rosin and rosin oil; and lignin sulfonates, and the like.
Rosin acid soap has been used with good success at a concentra~ion of about 5 percent by weight in the initial charge composition used in the synthesis of carboxylated elastomers. Of rosin acids, about 90 percent are isometric 25 wi-th abietic acid and the other 10 percent is a mixture of dehydro abie-tic acid and dihydro abietic acid.
The polymerization of these carboxylated rubbers may be initiated using free radical catalysts, ultraviolet light, or radiation. To insure a satisfactory polymeriz-30 a-tion rate, uniformity, and a con-trollable polymerization, free radical initiators are generally used with good results. Free radical initiators which are commonly used :lnclud~ -the various peroxygen compounds such as potassium persulfate,ammonium persulfate, benzoyl peroxide, hydrogen peroxide, di-t-butylperoxide, dicumyl peroxide, 2,L~-dichlorobenzoyl peroxide, decanoyl peroxide, lauroyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, t-butylhydro-peroxide, acetyl acetone peroxide, methyl ethyl ketone peroxide, succinic acid peroxide, dicetyl peroxydicarbonate, ~661~B

t-butyl peroxyacetate~ t-butyl pero ~naleic acid, t-'outyl peroxybenzoate, acetyl cyclohexyl sulfonyl peroxide, and the like; the various azo compounds such as 2-t-butylazo-2-cyanopropane, dimethyl azodiisobu'cyrate, azodiisobutyro-nitrile, 2-t-butylazo-1-cyanocyclohexane, l-t-amylazo-l-cyanocyclohexane, and the like; the various alkyl perketals, such as 2,2-bis-(t-butylperoxy)butane, ethyl 3,3-bis(t-butyl-peroxy)butyrate, 1,1-di-(t-butylperoxy) cyclohexane, and the like. Cumene hydrope~oxide can be used as an initiator to obtain very good results in the polymerization of carboxylated ni-trile.
The emulsion polymerization system used in the synthesis of carboxylated rubbers can be treated at the desired degree of conversion with shortstopping agents, such as hydroquinone. Typical shortstopping agents will not interfere with the action o~ succinic anhydride derivatives as scorch inhibitors. Typical stabilizing agents and standard antioxidants can also be added to the emulsion of a carboxylated rubber without interfering with the action of succinic anhydride derivatives as scorch inhibitors.
After the emulsion polymerization has been completed, many conventional coagulating techniques can be employed.
Normally such latexes are` coagulated wi-th reagents which insure the preservation of the carboxyl groups of the 25 elastomers as acidic moieties. Coagula-tion with acids or blends of salts with acids is usually very satisfactory.
For example, sulfuric acidj hydrochloric acid, blends of sodium chlorlde with sulfuric acid, and blends of hydro-chloric acid with methanol are very effective as coagulating agents for carboxylated rubber emulsions. Calcium chloride solution8 which are free of calcium hydroxide have also been used as coagulants with great success.
~ fter aoagulation washing may be employed to remove exces8 soap and/or electrolyte from the carboxylated 35 rubber~ Sometimes washing is also useful in adjusting the pH of the carboxylated elastomer that has been syn-thesized. After washing, if it is desired, the elastomer can be dewatered. If it is desirable -to do so, the ~2~

carboxylated rubber can also be dried and baled a~ter dewatering using conventional techniques.
Normally, a metal oxide (zinc oxide, magnesium oxide, copper oxide, calcium oxide or nickel oxide) usually zinc oxide 9 iS mixed into a carboxylated rubber af*er it has been dried and baled. Usually from about 0.5 to 10 parts of the metaloxide per hundred parts rubber (phr) is employed. Excellent results are obtained using about 5 phr of zinc oxide. This process o~ mixing the zinc oxide into the rubber is usually carried out by utilizing a Banbury mixer; however, any other procedure that will adequately mix the zinc oxide with the carboxylated rubber can also be employed. Normally, it is advantageous to minimize the time period between the point when the zinc oxide is added and the time at which the carboxylated rubber will be vulcanized (cross-linked). By minimizing this time period the amount of time in which spontaneous cross-linking between carboxyl groups can occur is mini-mized. Since unwanted cross-linking (scorch) often occurs in processing equipment (sometimes due to heat buildup) before it is desired, the time at which the metal oxide is added is not a total solution to the problem.
By distributing (mixing) alkenyl succinic anhydrides, alkyl succinic anhydrides, and their corresponding dicar-boxylic acids throughout a carboxylated rubber a scorchresistant car~oxylic rubber composition is produced with the problem o~ premature cross-linking (scorch) being greatly reduced. These succinic anhydride derivatives can be mixed into dried rubber using any procedure that ~ will resul-t in a thorough mixing. Good results have been obtained by mixing alkenyl succinic anhydrides into dried ~ubber with a Banbury mixer. Alkenyl succinic anhydrides having the ~-tructural ~ormula: 0 R - CH - C
~5 1 \ 0 CH2 ,C, wherein R is an alkenyl moiety containing from 8 to 25 carbon atoms, inclusive, are very useful as scorch inhib-itors for carboxylated rubbers.

Z066~9~
g The dicarboxylic acids corresponding to these alkenyl succinic anhydrides which have a general structural ~ormula:
R - CH - COOH
~H2 ~ COOH
wherein R is an alkenyl moiety containing from 8 'co 25 carbonatoms, inclusive, are also very effective as scorch inhibitors. These dicarboxylic acids are formed when alkenyl succinic anhydrides are added to water.
Mixtures of alkenyl succinic anhydrides with the general structural formula shown above wherein R is an alkenyl moiety containing from 12 to 17 carbon atoms have been used with excellent success as scorch inhibitors in carboxylated rubber. In such a mixture o~ alkenyl succinic anhydrides there will be a distribution of alkenyl succinic anhydride molecules containing varying numbers of carbon atoms in their R substituent groups ranging from 12 to 17, inclusive.
Alkyl succinic anhydrides which have the structural formula:
O
Z - CH - C

CH C
wherein Z is an alkylmoiety containing from 8 to 25 carbon atoms, inclusive, can also be mixed into dried rubber with a Banbury mixer to provide excellent scorch safety. Mix-tures of alkyl succinic anhydride molecules containing vary-ing numbers of carbon atoms in their Z substituent groupsranging from 8 to 25, inclusive, can also be mixed into carboxylated rubbers to provide excellen-t scorch resistance.
The dicarboxylic acids corresponding to these alkyl succinic a~hydrides are also very effective when aclded individually ~5 or as mixtures with varying Z substi-tuents to carboxylated rubbers. All of these aforementioned succinic anhydride derivatives and their corresponding dicarboxylic acids can be used alone or as mixtures to provide scorch resis-. tance when distributed throughout carboxylated rubbers.

ZOG611!31!~
10Alkyl succinic anhydrides (and their corresponding dicarbox-ylic acids) with the structural formula shown above wherein Z
is an alkyl moiety containing from 12 to 17 carbon atoms, i-n-clusive, can be employed to provide outstanding scorch safety 5 for carboxylated rubbers.
Alkenyl succinic anhydrides, alkyl succinic an'nydrides, and -their corresponding dicarboxylic acids may also be mixed into the emulsion of a carboxyla-ted rubber (prior to coagula-tion). By adding these succinic anhydride derivatives directly lG to the emulsion used in the polymerization of the rubber, excellent mixing will result. This procedure will provide excellent scorch safety, as is obtained when the succinic anhy-dride derivatives are mixed into dried rubber utilizing the Banbury mixer.
These succinic anhydride derivatives will provide excellent scorch safety for a carboxylated rubber at a concentration of about 5 parts per hundred parts of rubber (phr) by weight. It will usually be desirable to use lesser amounts of these agents since in lower concentrations they can also provide adequate 20 scorch safety. It is contemplated that for most carboxylated rubbers a concentration of succinic anhydride derivatives from about .1 -to about 1.5 phr would provide very satisfactory scorch resistance for most applications. The optimum amount of succinic anhydride derivatlves needed will vary with the degree 25 of carboxylation in the rubber being treated and with the pro-cessing conditions that will ultimately be employed in manu-facturing the rubber into useful products.
This invention is illustrated by the following represent-ative examples which are merely for the purpose of illustra-tion and are not to be regarded as limiting the scope of the inven-tion or -the manner in which it may be practiced. Unless speci.~ically indicated otherwise, parts and percentages are ~iven by weight.

~5 In order to demonstrate the superiority of succinic anhydride derivatives as scorch inhibitors when compared to other carboxylic acids and anhydrides a direct compar-ison between the scorch safety provided by a mixture of various alkenyl succinic anhydrides and numerous other -` ~2~6~3 ll carboxylic acids and anhydrides was experimentally made.
The mixture of alkenyl succinic anhydrides used in this comparison, hereinafter re~erred to as ASA, had the following structural formula:
5ClmH2m+1 0 CnH2n+l CH = CH ~ CH - C
/ o o wherein m + n equals 12 to 17. In this mixture of alkenyl succinic anhydrides there is a distribution of alkenyl succinic anhydride molecules with values for m and n varying ~rom O to 17, inclusive, and with the sum of m ~ n ranging ~rom 12 to 17, inclusive. ASA
is a liquid that is very soluble in most organic solvents, : e.g. acetone, benzene, and petroleum ether and is insoluble ; in water.
The structural formulas o~ the anhydrides and carboxylic acids used in these examples is shown below:

CH3(CH2)16 COOH

25Stearic Acid ~ C

Ph-thalic Anhydride 30 HO-CI-COOH (ClH2)8 (~CH2)2 CH~-COOH COOH COOH

Citric Acid Sebacic Acid Succinic Acid ~æ~ ?~

,, O
o c~c ~c o (CH2)l5 3~ ,c~

5 3,3',4 9 4'-Benzophenone- n tetracarboxylic Dianhydride Gulf PA-18 (BTDA) or 4,4'-Carbonyldiph-thalic Anhydride Gulf PA-18 is a polymerized anhydride resin derived from l~octadecene and maleic anhydride with a molecular weight of approximately 50,000.
A carboxylated nitrile rubber was used for these examples. The charge composition used in the synthesis of this carboxylated nitrile rubber was 200 parts deionized water,0.42 parts potassium hydroxide, 2.46 parts dodecyl-benzene sulfonic acid, .3 parts sodium acid phosphate, O.lparts tetrasodium ethylene diamine tetraacetate, 7 parts methacrylic acid, .45 parts tertiary dodecylmer-captan, 27 parts acryloni-trile, .03 parts cumene hydro-peroxide, 66 parts butadiene, .02 parts sodium formalde-hyde sulfoxylate,and 0.001 parts chelated ferrous sulfate.
In the preparation of this charge composition the potassium hydroxide and dodecyl benzene sulfonic ~cid were premixed wi-th 196 parts of deionized water and allowed to reac-t for 15 minutes before adding the other components of the charge composition. The sodium formaldehyde sulfoxylate and chelated ferrous sulfate activators were premixed in a separate vessel in 4 parts of deionized water before they were added to the main reaction vessel and mixed with the other components in the charge composition.
This polymerization was run in a 75.7 li-ter reactor with agitation by two 15.2 cm Brumagim mixers at 300 rpm's (revolutions per minute). This polymeriza-tion was run at a temperature of 21C (70F). This temperature was maintained for 10 hours a-t which time the solid content of the emulsion had reached 27.7 percent. At this point, %~
1~
the reaction had reached approximately 80 percent con~re-r-sion and .1 parts of sodium nitrite was added as a s~ort-stop. The emulsion was then degassed to remove ~poly~er-ized butadiene monomer that was present. This dega~sing was accomplished by applying 50.8 cm. o~ vacuum to the emulsion for lO hours.
Approximately 61.7 kilograms of latex was synthesized utilizing this polymerization recipe. 33.1 kilograms of this latex was mixed with emulsified Agerite Geltrol ; lO (2 active phr) and this blend was added to a solution o~
18.1 kg of sodium chloride and 710 grams of concentrated sulfuric acid in 272.2 kg.of water which was at a temper-ature of 60C. As this solution was vigorously agitated coagulation of the carboxylated nitrile rubber occurred.
The rubber crumb was dipped out of this aqueous solution and dewatered with a dewatering screw down to about 10 percent water. The rubber was then oven dried to under .5 percent moisture content. 7.7 kilograms of dried rubber was produced by this process. A Banbury

2~ mixer was employed to add 50 parts of carbon black and

3 parts of various scorch inhibiting agents per lO0 parts rubber (phr).
A Midget Banbury Mixer manufactured by Farrel Corporation was used for these examples. The Banbury was run at a speed of 84 rpm's and the rubber was mixed (by itself) for an initlal breakdown period of one minute.
After this initial breakdown period the carbon black and scorch inhibiting agent being tested were added and mixed for a period of 3 minutes. This technique made a very ; 30 good mixture of the rubber, carbon black and scorch inhibiting agent being tested. Two parts tetramethyl th~uram disul~ide, l part n-oxydiethylene benzothiazole-2-sul~inamide, 5 par~s zinc oxide, and .3 parts sulfur per lO0 parts rubber (phr) were mill mixed using a ~5 rolling bank into the rubber for one minute followed by 10 additional passes through the mill mixer.

..

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These samples containing the di~fe-rent scor^h lnhibiting agen-ts were then tested to determine their Mooney Scorch values. Mooney Scorch values for rubber samples containing each of the eight aforementione~
scorch inhibiting agents to a 5 and 10 point rise in Mooney Scorch were determined at an operating ternper-ature of 121C (250F) using ASTM Method Dl077. The values that were determined for a 5 and lO point rise in Mooney Scorch (designated as T-5 and T-lO, respectively) are given in Table I.
- TABLE I

Exam~le A~ent _ (min.) (min.) l ASA 39 >~9 2 Stearic Acid 8.3 9.8 3 Phthalic Anhydride 2.3 2.9

4 Citric Acid 9.1 14.0 Sebacic Acid 6.2 7.9 6 Succinic Anhydride .6 .8 7 BTDA 7.8 11.6 T-5 scorch values of 15 minutes or greater are generally considered necessary for adequate scorch safety. As can be determined by examining Table I, ASA is the only agent in the example that provides greater than 15 minutes of Mooney Scorch protection. When ASA was used as a scorch inhibiting agent i-t took over four times as long to reach a5Foint rise in Mooney Scorch than it did when any other agent was used as a scorch inhibitor. The time to a 10 point rise in Mooney Scorch when ASA was employed was over 2--1/2 times as long as when any o-ther scorch in-hlbLt:lng agent -tested was employed. I-t is readily apparen-t that ASA is va,stly superior to any other carboxylic acid or anhydr:Lde as a scorch inhibi-tor.
Some ,speci:~ic compounds that are represen-ta-tive of those presen-t in ASA include l-dodecenyl succLnic anydride, l-hep-tadecenyl succinic anhydride, l-me-thyl-l-hexaclecenyl succinic anhydride, l-methyl-l-undecenyl - ~o~

succinic anhydride, l-pentyl-l-heptenyl succinic anhydride, l-heptyl-l-octenyl succinic anhydride, l-butyl-l-decenyl succinic anhydride. The position of the double bond and side chains in alkenyl succinic anhydrides is unimportant and excellent scorch safety will be provided by such alkenyl succinic anhydrides containing from 12 to 17 carbon atoms. Some representative examples of such alkenyl succinic anhydrides include l-pentyl-3-octenyl succinic anhydride, l-butyl-6-decenyl succinic anhydride, 2,3,5-trimethyl-4-propyl-2-heptenyl succinic anhydride, 2,4-diethyl-6-dodecenyl succinic anhydride, 3,3-dipropyl-~-decenyl succinic anhydride. Good scorch safety is also provided by alkenyl succinic anhydrides containing from 8 to 25 carbon atorns. Some representative examples of ]5 such alkenyl suecinic anhydrides include 2--octenyl succinic anhydride, 6-pentacosenyl succinic anhydride, 2-ethyl-4-hexenyl succinic anhydride, 3,3-dipropyl-7-heptadecenyl succinic anhydride. Alkyl ~uccinic anhydrides containing from 12 to 17 carbon atoms are generally effective in providing scorch resistance for carboxylated rubbers.
Good scorch sa~ety is also provided by alkyl succinic anhydrides containing from 8 to 25 carbon atoms. Some representative examples of such alkyl succinic anhydrides inelude oetyl sueelnie anhydride, nonyl sueeinie anhydride, dodeeyl sueeinie anhydride, eicosyl succinic anhydride, pentacosyl succinic anhydride, 2,2-dibutyldecyl succinic anhydride, 4-ethyl-3,3-dimethylheptyl succinic anhydride, 4-isobutyl-2,5-dimethyltetradecyl succinic anhydride.
Alkyl and alkenyl sueeinic anhydrides ean be used alone or 3~ ln any eor~blnation with other alkyl and alkenyl sueeinie anh~drldes to provide seoreh sarety in earboxylated rLIbbers. The a~orementloned representative examples of t;hese al~yl and alkenyl sueeinic anhydrides are not meant to be limiting upon the group that will be effective in providin~ seorch resistance and eertainly do not represent an exhaustive list of the eompounds that ean be employed.

~ ., ~20 While certain representative embodiments and details have been shown for the purpose of illust-rating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made ; 5 therein without departing from the scope of the invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An improved scorch resistant carboxylic rubber composition comprising:
(a) a carboxylated rubber; and (b) at least one succinic anhydride derivative selected from the group consisting of alkenyl succinic anhydrides having the structural formula:

wherein R is an alkenyl moiety containing from 8 to 25 carbon atoms, inclusive; dicarboxylic acids having the structural formula:

wherein R is an alkenyl moiety containing from 8 to 25 carbon atoms, inclusive; alkyl succinic anhydrides having the structural formula:

wherein Z is an alkyl moiety containing from 8 to 25 carbon atoms, inclusive; and dicarboxylic acids having the structural formula:

wherein Z is an alkyl moiety containing from 8 to 25 carbon atoms, inclusive; which is distributed throughout said carboxylated rubber composition as a scorch inhibitor.

2. An improved scorch resistant carboxylated rubber composition as specified in claim 1, wherein said R is an alkenyl moiety containing from 12 to 17 carbon atoms, inclusive.

3. An improved scorch resistant carboxylated rubber composition as specified in claim 1, wherein said Z
is an alkyl moiety containing from 12 to 17 carbon atoms, inclusive.

4. An improved scorch resistant carboxylated rubber composition as specified in claim 2, wherein said R has the structural formula:

wherein m + n equals 12 to 17.

5. An improved scorch resistant carboxylated rubber composition as specified in claim 1, further comprising a metal oxide which is distributed throughout said carboxylated rubber composition.

6. An improved scorch resistant carboxylated rubber composition as specified in claim 5, wherein said metal oxide is a member selected from the group consisting of zinc oxide, magnesium oxide, copper oxide, calcium oxide, and nickel oxide.

7. An improved scorch resistant carboxylated rubber composition as specified in claim 6, wherein said metal oxide is zinc oxide.

8. An improved scorch resistant carboxylated rubber composition as specified in claim 1, wherein said carboxylated rubber is a member selected from the group consisting of terpolymers of methacrylic acid, styrene, and butadiene; terpolymers of methacrylic acid, acrylonitrile, and butadiene; terpolymers of acrylic acid, acrylonitrile, and butadiene;
terpolymers of methacrylic acid, vinylidene chloride, and butadiene; copolymers of methacrylic acid and butadiene; and copolymers of methacrylic acid and isoprene.

9. An improved scorch resistant carboxylated rubber composition as specified in claim 8, wherein said carboxylated rubber is a terpolymer of methacrylic acid, acrylonitrile, and butadiene.

10. An improved scorch resistant carboxylated rubber composition as specified in claim 1, wherein the total concentration of said succinic anhydride derivatives is less than about 5 phr.

11. An improved scorch resistant carboxylated rubber composition as specified in claim 10, wherein the total concentration of said succinic anhydride derivatives is about .1 to about 1.5 phr.

12. A process for improving the scorch resistance of a carboxylated rubber comprising, distributing throughout said carboxylated rubber a chemical agent selected from the group consisting of alkenyl succinic anhydrides having the structural formula:

wherein R is an alkenyl moiety containing from 8 to 25 carbon atoms, inclusive; dicarboxylic acids having the structural formula:

wherein R is an alkenyl moiety containing from 8 to 25 carbon atoms, inclusive; alkyl succinic anhydrides having the structural formula:

wherein Z is an alkyl moiety containing from 8 to 25 carbon atoms, inclusive; and dicarboxylic acids having the structural formula:

wherein Z is an alkyl moiety containing from 8 to 25 carbon atoms, inclusive; which is distributed throughout said carboxylated rubber composition as a scorch inhibitor.

13. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 12, wherein said chemical agent is distributed through-out said carboxylated rubber by mixing said chemical agent into the emulsion of said carboxylated rubber prior to coagulation.

14. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 12 wherein said agent is distributed throughout said carboxylated rubber which has been dried by mixing it into said carboxylated rubber utilizing a Banbury mixer.

15. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 12 wherein said R is an alkenyl moiety containing from 12 to 17 carbon atoms, inclusive.

16. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 12 wherein Z is an alkyl moiety containing from 12 to 17 carbon carbon atoms, inclusive.

17. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 12 wherein said R has the structural formula:

wherein m + n equals 12 to 17.

18. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 12 further comprising a metal oxide which is distributed through-out said carboxylated rubber composition.

19. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 18 wherein said metal oxide is a member selected from the group consisting of zinc oxide, magnesium oxide, copper oxide, calcium oxide and nickel oxide.

20. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 18 wherein said metal oxide is zinc oxide.

21. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 12 wherein said carboxylated rubber is a member selected from the group consisting of terpolymers of methacrylic acid, styrene, and butadiene; terpolymers of meth-acrylic acid, acrylonitrile and butadiene; terpolymers of acrylic acid, acrylonitrile, and butadiene; ter-polymers of methacrylic acid, vinylidene chloride, and butadiene; copolymers of methacrylic acid and butadiene; and copolymers of methacrylic acid and isoprene.

22. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 12 wherein said carboxylated rubber is a copolymer of methacrylic acid, acrylonitrile and butadiene.

23. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 12, wherein the total concentration of said succinic anhydride derivatives is less than about 5 phr.

24. A process for improving the scorch resistance of a carboxylated rubber as specified in claim 23, wherein the total concentration of said succinic anhydride derivatives is about .1 to about 1.5 phr.